In the field of air navigation, an aircraft trajectory comprises a horizontal dimension and a vertical dimension. The skeleton outline of the horizontal trajectory of an aircraft is called route which consists of a sequence of flight plan points joined by segments. Each of these segments is defined between two waypoints, the end waypoint of a segment also forming the initial waypoint of the next segment of the route. The waypoints can for example be defined by the location of radio navigation beacons, or by geographic coordinates.
For air navigation, an aircraft generally determines its trajectory by following a route and a vertical trajectory calculated in advance. The reference route can for example be a pre-calculated standard route, or a route calculated by a flight management computer to best link a starting point and an arrival point. In this case, the aircraft successively follows each of the segments of the route. When it follows one of the segments of the route, its objective is the end waypoint of said segment. As soon as it has passed this waypoint, it follows the next segment. The action of selecting a new waypoint to be followed is called sequencing from the current waypoint. The segment followed at a given instant is called active segment.
The aircraft generally operates in a so-called managed guidance mode, a mode in which its horizontal trajectory automatically follows the reference route. In this mode, the aircraft is locked onto the route, in other words guidance laws are applied to the aircraft in order for it to follow the route step by step. However, the aircraft can sometimes deviate from the reference route. For example, it can deviate from the reference route if air traffic control instructs it so for safety reasons.
A flight management computer according to the prior art does not provide any method for permanently proposing a satisfactory re-joining trajectory when the aircraft deviates from a reference route. Indeed, the only indication provided by a flight management computer according to the prior art is a straight-line distance with respect to the next waypoint. However, this distance does not indicate if the waypoint will be able to be reached in satisfactory conditions. The patent FR2921152 proposes a method for assisting in re-joining a route. This patent describes a method for automatically selecting a waypoint to be re-joined when an aircraft is no longer in managed mode. However, this method does not make it possible to calculate the re-joining trajectory itself. It is not therefore permanently executed for the aircraft to permanently have a proposition of trajectory to be followed without the intervention of a pilot.
The object of the invention is to go beyond the limitations of the prior art. Its aim is notably a method for permanently proposing a continuous, flyable re-joining trajectory for a reference route of an aircraft, recalculated periodically at each new position of the aeroplane.